Understanding Frost
Total Page：16
File Type：pdf, Size：1020Kb
Understanding Frost From Cornell Cooperative Extension, Chemung County More gardening information at www.gardening.cornell.edu In spring and fall, the very mention of frost on the hilltops, while the hillsides are frost-free. sends gardeners scurrying for sheets, boxes, On any given property, there may be jars, floating row covers, the sprinkler system, temperatures on different sides of the house, or whatever they can scrounge to keep their under protective trees, on south or north facing plants safe from a possible cold snap. Just slopes, or in low-lying spots. what is frost, and what does it do? How do your protective measures work? Frost warnings signal us that our plants may be in trouble. However, the essential criterion in There are two types of frost, advective and damaging plants is not the appearance of frost, radiation. Advective frosts occur when a cold but the internal temperature in various tissues front sweeps into an area. Winds are typically of the plant. If this is cold enough to break cell gusty, clouds may occur and the thickness of walls or disrupt cell constituents beyond repair, the cold air layer may reach more than a mile damage, wilting, and death will occur in high. One seldom sees the first frost of the affected tissues. Frost will not always cause season under these conditions. The first frost this degree of chilling within plant tissue, nor is is typically a radiation frost. These occur under it the only cause. a clear sky and calm winds. Typically, we may have 3 to 5 weeks of good On overcast nights, cloud cover acts like a weather following a frost but the crops have blanket on the Earth, trapping radiant heat from already been damaged or killed. Rather than the ground. Any wind mixes the air thus just talking about the weather, there are trapped, creating a uniform temperature. several things that gardeners can do to However, clear skies and calm winds allow minimize the effects of the first radiation frost. radiant heat from the Earth to rise to the upper These include: layers of the atmosphere. Lack of wind prevents mixing of the air and an inversion Watch the calendar and the forecast – Know layer develops. An inversion means that when the average first fall frost will be in your atmospheric conditions are inverse or opposite area. This is the date by which a frost will of normal daytime conditions when air occur 50% of the time. In looking over weather temperature decreases with height. In an records in upstate New York over the past 50 inversion, cold air collects near the ground years, it seems that this date is coming later in while warmer air lies above this trapped cold fall each decade (although the date of the last layer. spring frost has not changed much). Keep a careful eye on the weather forecast too. Cool, The topography of the land also affects frost clear nights with low humidity, often following a prevalence. Cool air settles at the bottom of cold front, are signs of an impending frost. slopes because it is heavier than warm air. Frost pockets will then form in valleys where Beware the Full Moon? – People have always cool air is trapped. Higher altitudes also have associated the full moon with an increased colder temperatures. Therefore you are apt to chance of frost. However, in reviewing weather see frost damage at the bottom of slopes and records of four locations in the Northeast for Helping You Put Knowledge to Work Cornell Cooperative Extension provides equal program and employment opportunities. NYS College of Agriculture and Life Sciences, NYS College of Human Ecology, and NYS College of Veterinary Medicine at Cornell University, Cooperative Extension associations, county governing bodies, and U.S. Department of Agriculture, cooperating. the last 100 years, a full moon did not increase gram of water that freezes. Therefore, the chance of a frost. It was just as likely to watering plants before they are injured from occur when no moon was present as when the frost can help keep their internal temperature moon was full! above freezing. A single application at the coldest part of the night (generally just before Harvest early – A crop like tomatoes is very sunrise) may be enough on 30- to 32-degree F sensitive to frost. If you have no way to protect nights. On colder nights it may be necessary plants, you may want to harvest all fruit that are to apply overhead irrigation for an extended in the mature green stage of ripening. Fruit period of time, allowing actual ice formation on harvested at this stage will still ripen, albeit not the plants. In this case, irrigation must with the same flavor as fruit harvested with continue until morning temperatures rise above some color. Place fruit in a single layer in a 32 F and the ice melts. It is important to note warm, dark location with some air movement. that once frost damage occurs, watering does Tomatoes and other fruit do not need light to not help. ripen. In fact, light will slow ripening. Store where the temperature does not go below Chemical sprays – Buyer beware! Many 55 F. Lower temperatures will cause the fruit materials will claim to provide frost protection to be poorly flavored. using a variety of techniques. However, no commercially available product seems to be Irrigate before the frost – A moist soil can able to stand up to a replicated, scientific test. hold four times more heat than a dry soil. It will also conduct heat to the soil surface faster than Heaters and wind machines – These a dry soil, aiding in frost prevention. In a study measures are generally restricted to performed years ago, the air temperature commercial growers and work best in orchards. above a wet soil was 5 degrees F higher than Both are used to break down an inversion that above a dry soil and the difference was layer. Heaters warm the cold ground air, maintained until 6 a.m. the next morning. causing it to rise. This updraft causes a Thus, plants should be well watered the corresponding downdraft, thus mixing the air. evening before a frost. Wind machines are huge fans mounted on thirty-foot towers. The wind currents they Cover your plants – Covering plants can give create physically mix the warm and cold air you 2 to 5 degrees F protection. The covers layers. can be laid right over the crop, or can be supported on stakes. The difference being that Whatever frost protection measures we use, protection is less wherever the cover touches winter will eventually end our growing season. the plant. Any material can be used to cover The time will come to say goodbye to our the plants, however woven fabrics are better garden and begin chores left undone for so insulators then plastics or paper. The best long under the pretext that, “there will be more time to apply covers is in the late afternoon time in winter!” after the wind has died down. Remove covers the next morning before the sun hits them. Compiled by Eric de Long Chemung 9/01 References Irrigate during the potential frost – Many people claim that watering the frost off plants Reiners, Stephen. Preventing Damage from an Early prevents frost damage. This is partially true. Frost. Cornell University Consumer News Service. As mentioned above, watering plants helps September, 2001. raise their temperature and the air around them Anonymous. Understanding Frost. Cornell Cooperative to that of the water. In addition, as water Extension of Albany County fact sheet. 1995. freezes, heat is released; 80 calories for each Understanding frost, page 2 .